Application of the hottest variable frequency spee

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Application of frequency conversion and speed regulation technology on portal crane

our company has two 5T portal cranes used for PTA loading, which mainly undertake the loading task of PTA of Yangzi Petrochemical. Its electrical speed regulation system adopts the old-fashioned speed regulation mode of winding type asynchronous motor rotor circuit in series resistance. Due to the extremely high working frequency (the duration rate is higher than 40%), faults such as burning and adhesion of contactor contacts, misoperation of overcurrent relay, damage to starting resistance, and burning out of motor winding often occur. The company decided to purchase two new 5T gantry cranes and adopt full frequency conversion speed regulation technology for the electrical speed regulation system

1 inverter selection scheme

select ABB's inverter acc600 (acs601) dedicated to hoists. The frequency converter adopts advanced DTC control mode and is specially used for the lifting mechanism of crane

the capacity of the frequency converter of the lifting mechanism and luffing mechanism is selected according to the rated output current inv of the frequency converter, that is, 1.2 ~ 1.5 times the rated current of the motor. The capacity of the frequency converter of the rotating mechanism (traveling mechanism) should be appropriately increased according to the actual operation. Since ABB frequency converter manufacturer has matched the frequency converter, braking unit and braking resistor, it is only necessary to select the corresponding frequency converter model

2 control mode

in order to meet the habitual operation of operators on portal cranes, we adopt the operation control mode of a PLC and master controller from GE company. Considering that the acs601 frequency converter can store two sets of independent motor parameters and control methods, and the total power of four motors of the traveling mechanism is equal to that of one motor of the rotating mechanism, both of which are 30 kW, the rotating mechanism and the traveling mechanism will share one frequency converter in the design, with rotation as the main and walking as the auxiliary, which is selected and controlled through two contactors and one change-over switch. This not only saves investment, but also conforms to the operating regulations that the walking and rotating mechanisms cannot act at the same time. The fault monitoring system adopts the combination of PC monitoring machine and touch screen, and is designed with dynamic data monitoring (including motor current, voltage, torque, etc.), historical data and fault recording functions, status monitoring functions of various components, etc

3 system control

the block diagram of system control is shown in Figure 1

4 problems and solutions in use

during the commissioning and operation of the crane, the frequency converter of the rotating mechanism often gives an overcurrent alarm, while other equipment operates well. After careful observation and data measurement on site, we found that the overcurrent alarm occurred during the starting process of the rotating mechanism, and the operation process after the starting of the rotating mechanism was normal. The frequency converter showed that the operating current of the motor was below the rated current of the motor, while the starting current of the motor reached about twice the rated current. After analysis, we believe that the mechanical inertia of the rotating mechanism is relatively large, which increases the starting torque of the motor. In addition, the working condition requires that the starting time of the rotating mechanism should not be too long (the starting time of the motor set by the frequency converter is 3S), which makes the starting current of the motor of the rotating mechanism larger, reaching about twice the rated current of the motor. The parameter 30.07 (maximum limit of motor current) of ABB Inverter acs601 can only be adjusted to 1.5 times the rated current of the motor at most, so the inverter has an overcurrent alarm. Solutions:

(1) increase the capacity of the motor. However, replacing the motor requires changing a large number of mechanical equipment of the crane, which is not only expensive, but also difficult

(2) increase the capacity of frequency converter. When selecting the frequency converter, we have considered the factor that the starting torque of the rotating mechanism is relatively large, so we have left enough margin. The motor of the rotating mechanism is 30 kW, and the frequency converter is ACS (generally used for 55kW Jinan testing machine after-sales service motor, with a rated current of 112 A)

therefore, we increased the parameter 99.06 (motor rated current) of ABB frequency converter acs601 from 60A to 80A, and adjusted the parameter 30.07 of frequency converter acs601 to the maximum 150%, so that the starting overload coefficient of the motor reached about twice, which not only met the requirement that the starting overload coefficient of the crane motor was not greater than 2.5, but also did not exceed the rated current of the frequency converter 112a. At the same time, the over-current alarm of the frequency converter has also been solved, Other protection functions of the frequency converter to the motor have not been affected (Note: it is not recommended to change the motor parameters in the frequency converter arbitrarily. Some parameters can be fine tuned only when the capacity of the motor and frequency converter is confirmed to be large enough and the working conditions permit. Otherwise, it is easy to cause problems in motor identification and modeling. The traditional EPDM ethylene propylene rubber is produced with petroleum based raw materials ethylene and propylene, and ultimately affects the control performance of the frequency converter)

5 use effect

(1) adopting variable-frequency cage motor to replace wound motor avoids the fault problems caused by collector ring, brush and starting resistance, improves the utilization rate of equipment and saves a lot of maintenance costs

(2) the number of contactors in the main circuit is reduced from the original 20 to 2. The electronic over-current relay inside the frequency converter is used to replace the traditional over-current relay, avoiding misoperation, reducing fault points, and improving the reliability of system operation

(3) the whole machine control system adopts programmable controller (PLC is used for control, and a fault monitoring system is added. The friendly man-machine interface is composed of PLC and gp2500 touch graphic display. The location of the fault and the simple treatment method are displayed in real time by graphics and text ----- Dr. Liu Yiwu of the Packaging Research Institute of Hunan University of technology to monitor the operation or stop state of the main electrical components, which improves the efficiency of the maintenance personnel in eliminating electrical faults.

(4) The starting and mechanical characteristics of the motor are improved, the whole machine runs more smoothly and reliably, and the safety of the system is improved

6 problems that should be paid attention to

the frequency conversion control system is not as flexible as the original control system, and there is a lag phenomenon. If the deep-water berths, channels and anchorages of cranes in Hainan will be built in an orderly manner, with high operating frequency and many inching, the starting current is also large due to the large starting inertia of the rotating mechanism. Therefore, the rotating mechanism can still adopt the speed regulation method of the rotor circuit series resistance of the original wound asynchronous motor, while the comprehensive effect of other mechanisms using the frequency conversion speed regulation system will be better. If the rotating mechanism also adopts the variable frequency speed regulation system, enough margin should be left in the selection of frequency converter capacity. One frequency converter controls multiple motors (for example, the rotating mechanism motor and the traveling mechanism motor share one frequency converter). The electromagnetic contactor set on the output side of the frequency converter should avoid acting when the frequency converter is output when designing the peripheral circuit. (end)

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